Note 33 — THE FYRST PART OF THE NAUIGATION INTO THE NORTH SEAS.

Graedt-boogh—rendered Radius astronomicus in the Amsterdam Latin version of 1598, and Ray nautique in the French version of the same year and place—Cross-staff, Jacob’s-staff, or fore-staff; a well known instrument, no longer in use among European navigators. But the Arab seamen on the east coast of Africa still employ a primitive instrument, which is essentially the same. It consists of a small quadrangular board, through which a string, knotted at various distances, is passed; each knot being at such a distance from the board, that when the latter is held by the observer before him, with the knot between his teeth and the string extended, the board (between its upper and lower edges) shall subtend the angle at which the pole-star is known to be elevated above the horizon at some one of the ports frequented by the observer. Inartificial as such an instrument may be, yet if, instead of a knotted string, a notched stick were used, on which the board might slide backwards and forwards, it would be the cross-staff of our early navigators. ↑